This invention relates generally to the detection of unknown laser sources and more particularly to a method involving stimulated photoluminescence of pretreated solid state phosphor material to effect detection without frequent recharging or respotting of laser beam impingement with respect to near infrared lasers.
The use of alkaline earth sulfides, doubly doped with rare earth ions for solid state photoluminescent sensors to detect and discriminate between infrared lasers of the near and far type is disclosed in copending application U.S. Serial No. 385,032 filed Jul. 25, 1989. Such type of photoluminescent sensors utilized for detection purposes only, are marketed for example by Quantex Corporation of Rockville, Md. as disclosed in its U.S. Pat. Nos. 4,806,772 and 4,822,520 to Lindmayer.
The use of alkaline earth oxides as a luminescent material excited by ultraviolet radiation is also known, as disclosed for example in U.S. Pat. No. 4,806,825 to Catherall et al. and U.S. Pat. No. 4,751,148 to Popma et al. According to U.S. Pat. No. 4,427,570 to Chen et al., thermochemically reduced alkaline earth oxides, including magnesium oxide, have F center luminescence that is long lived near room temperature becuase of the presence of H.sup.- ion electron traps. The latter patents do not expressly suggest use of MgO in sensors for detection of and discrimination between unknown external laser sources based on stimulated photoluminescence emissions.
The use of solid state luminescent material excited to emit visible light after discontinuance of excitation was also known as indicated in column 1, lines 38-41 of U.S. Pat. No. 4,195,226 to Robbins et al. According to the Robbins et al. patent, relatively long periods of luminescence after discontinuance of excitation, was deemed to be undesireable in the associated applications. The photoluminescent material was therefore prepared in such a manner as to obtain rapid fading of the externally excited emissions, as stated in column 1, lines 42-46 of the Robbins et al. patent, in order to enhance collection of data.
It is therefore an important object of the present invention to provide an improved method of detecting and discriminating between unknown sources of laser beam radiation for military and commercial purposes.
It is another important object of the present invention in accordance with the foregoing object to provide a sensor utilitizing photoluminescent sensing material which may be stimulated, after being charged, by external radiation in the invisible spectral range to detect and discriminate between different unknown laser sources of such external radiation, and wherein the charging of the sensing material involves a charge trapping condition in which stimulation is limited to near and far infrared lasers.